1. Field of the Invention
This invention relates generally to gas sensors, and, more specifically to miniaturized sensors for the detection of very low levels of ambient gases, especially hydrogen.
2. Background Prior Art
There are analytical tools today which are capable of qualitatively and quantitatively detecting very small amounts of gases. These include relatively expensive and large laboratory tools with sensitivity for spectroscopic analysis of a broad range of gas compositions (example: the quadrupole mass spectrometer), as well as miniaturized sensors that are optimized for the detection of the concentration of a particular type of gas molecule (example: an oxygen sensor in automobile emission control systems).
There are needs in the field to be able to detect the presence of very small amounts of specific gases. These needs include the detection of explosive or otherwise hazardous gases, such as in factories where industrial processes are required which use or produce hazardous chemicals. Also product quality control requires engineered feedback systems to regulate process parameters on the basis of detected gases. One ubiquitous example is the emissions control system that regulates operating parameters of automobile engines as a function of the concentration of oxygen gas that is detected in the exhaust via an oxygen sensor. In the home, where natural gas is used for heating, cooking, and the like, the need for gas sensors exist to prevent explosion hazards (from gas leaks) as well as to prevent buildup of toxic emissions such as carbon-monoxide gas.
The need for gas detection sensors that are simpler, less costly to produce, more compact, and consume less power, is ongoing. For example, availability of inexpensive and compact sensors for carbon-monoxide and natural gas would make the integration of warning systems into domestic heater thermostats possible, resulting in important public heath benefits. Similar benefits would result from integration of hazardous gas monitoring technology as a standard feature in consumer products such as cellular telephones. The role of hydrogen as a fuel to replace diminishing fossil fuels generates needs for hydrogen sensors in control- and warning systems.
It was recently reported that at least for hydrogen gas, certain materials undergo a change in their easy axis of magnetization as a function of the presence or absence of hydrogen, which property has been suggested could be useful for magnetization switches. See Physical Review Letters 93, 247203 (2004). Therein, a reversible switching of the easy axis of magnetization for Ni on Cu (001) from in-plane to out-of-plane was demonstrated, by changing the partial pressure of hydrogen in the gas phase around the sample. As used herein, the term “easy axis” refers to the energetically favorable direction of the spontaneous magnetization in ferromagnetic material.